Re: [PATCH] kvm: x86: move architecture-specific code into kvm_arch_vcpu_fault

[Sean Christopherson <seanjc@google.com>]

On Wed, Aug 11, 2021, Hou Wenlong wrote:
> The function kvm_arch_vcpu_fault can handle architecture-specific
> case, so move pio-data fault case into it for x86.
> 
> Signed-off-by: Hou Wenlong <houwenlong93@linux.alibaba.com>
> ---
>  arch/x86/kvm/x86.c  | 8 ++++++++
>  virt/kvm/kvm_main.c | 4 ----
>  2 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index e5d5c5ed7dd4..30b0706eced8 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5348,6 +5348,14 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
>  
>  vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
>  {
> +	if (vmf->pgoff == KVM_PIO_PAGE_OFFSET) {
> +		struct page *page = virt_to_page(vcpu->arch.pio_data);
> +
> +		get_page(page);
> +		vmf->page = page;
> +		return 0;
> +	}
> +
>  	return VM_FAULT_SIGBUS;

What about a prep patch (below) to refactor kvm_arch_vcpu_fault() to return
a struct page pointer instead of vm_fault_t?  That would simplify this patch to:

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8c1871f0211c..1c5d68ced3be 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5348,6 +5348,8 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 
 struct page *kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
 {
+       if (vmf->pgoff == KVM_PIO_PAGE_OFFSET)
+               virt_to_page(vcpu->arch.pio_data);
        return NULL;
 }
 
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index a75848799712..c3b1e8f55251 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3486,10 +3486,6 @@ static vm_fault_t kvm_vcpu_fault(struct vm_fault *vmf)
 
        if (vmf->pgoff == 0)
                page = virt_to_page(vcpu->run);
-#ifdef CONFIG_X86
-       else if (vmf->pgoff == KVM_PIO_PAGE_OFFSET)
-               page = virt_to_page(vcpu->arch.pio_data);
-#endif
 #ifdef CONFIG_KVM_MMIO
        else if (vmf->pgoff == KVM_COALESCED_MMIO_PAGE_OFFSET)
                page = virt_to_page(vcpu->kvm->coalesced_mmio_ring);


From 94ce06a001af4bd79635f1c8d681f560bca13cba Mon Sep 17 00:00:00 2001
From: Sean Christopherson <seanjc@google.com>
Date: Wed, 11 Aug 2021 11:28:03 -0700
Subject: [PATCH] KVM: Refactor kvm_arch_vcpu_fault() to return a struct page
 pointer

Refactor kvm_arch_vcpu_fault() to return 'struct page *' instead of
'vm_fault_t' to simplify architecture specific implementations that do
more than return SIGBUS.  Currently this only applies to s390, but a
future patch will move x86's pio_data handling into x86 where it belongs.

No functional changed intended.

Cc: Hou Wenlong <houwenlong93@linux.alibaba.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/arm64/kvm/arm.c       |  4 ++--
 arch/mips/kvm/mips.c       |  4 ++--
 arch/powerpc/kvm/powerpc.c |  4 ++--
 arch/s390/kvm/kvm-s390.c   | 12 ++++--------
 arch/x86/kvm/x86.c         |  4 ++--
 include/linux/kvm_host.h   |  2 +-
 virt/kvm/kvm_main.c        |  5 ++++-
 7 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index e9a2b8f27792..83f4ffe3e4f2 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c
@@ -161,9 +161,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	return ret;
 }

-vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
+struct page *kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
 {
-	return VM_FAULT_SIGBUS;
+	return NULL;
 }


diff --git a/arch/mips/kvm/mips.c b/arch/mips/kvm/mips.c
index 75c6f264c626..ecfbcfe00b78 100644
--- a/arch/mips/kvm/mips.c
+++ b/arch/mips/kvm/mips.c
@@ -1049,9 +1049,9 @@ int kvm_arch_vcpu_ioctl_set_fpu(struct kvm_vcpu *vcpu, struct kvm_fpu *fpu)
 	return -ENOIOCTLCMD;
 }

-vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
+struct page *kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
 {
-	return VM_FAULT_SIGBUS;
+	return NULL;
 }

 int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
diff --git a/arch/powerpc/kvm/powerpc.c b/arch/powerpc/kvm/powerpc.c
index be33b5321a76..b9c21f9ab784 100644
--- a/arch/powerpc/kvm/powerpc.c
+++ b/arch/powerpc/kvm/powerpc.c
@@ -2090,9 +2090,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 	return r;
 }

-vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
+struct page *kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
 {
-	return VM_FAULT_SIGBUS;
+	return NULL;
 }

 static int kvm_vm_ioctl_get_pvinfo(struct kvm_ppc_pvinfo *pvinfo)
diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
index 4dc7e966a720..eab9c4820185 100644
--- a/arch/s390/kvm/kvm-s390.c
+++ b/arch/s390/kvm/kvm-s390.c
@@ -4975,17 +4975,13 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 	return r;
 }

-vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
+struct page *kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
 {
 #ifdef CONFIG_KVM_S390_UCONTROL
-	if ((vmf->pgoff == KVM_S390_SIE_PAGE_OFFSET)
-		 && (kvm_is_ucontrol(vcpu->kvm))) {
-		vmf->page = virt_to_page(vcpu->arch.sie_block);
-		get_page(vmf->page);
-		return 0;
-	}
+	if (vmf->pgoff == KVM_S390_SIE_PAGE_OFFSET && kvm_is_ucontrol(vcpu->kvm))
+		return virt_to_page(vcpu->arch.sie_block);
 #endif
-	return VM_FAULT_SIGBUS;
+	return NULL;
 }

 /* Section: memory related */
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fdc0c18339fb..8c1871f0211c 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5346,9 +5346,9 @@ long kvm_arch_vcpu_ioctl(struct file *filp,
 	return r;
 }

-vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
+struct page *kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf)
 {
-	return VM_FAULT_SIGBUS;
+	return NULL;
 }

 static int kvm_vm_ioctl_set_tss_addr(struct kvm *kvm, unsigned long addr)
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 03f37e4def6f..7df730cdc935 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -1000,7 +1000,7 @@ long kvm_arch_dev_ioctl(struct file *filp,
 			unsigned int ioctl, unsigned long arg);
 long kvm_arch_vcpu_ioctl(struct file *filp,
 			 unsigned int ioctl, unsigned long arg);
-vm_fault_t kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf);
+struct page *kvm_arch_vcpu_fault(struct kvm_vcpu *vcpu, struct vm_fault *vmf);

 int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext);

diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
index 3e67c93ca403..a75848799712 100644
--- a/virt/kvm/kvm_main.c
+++ b/virt/kvm/kvm_main.c
@@ -3499,7 +3499,10 @@ static vm_fault_t kvm_vcpu_fault(struct vm_fault *vmf)
 		    &vcpu->dirty_ring,
 		    vmf->pgoff - KVM_DIRTY_LOG_PAGE_OFFSET);
 	else
-		return kvm_arch_vcpu_fault(vcpu, vmf);
+		page = kvm_arch_vcpu_fault(vcpu, vmf);
+	if (!page)
+		return VM_FAULT_SIGBUS;
+
 	get_page(page);
 	vmf->page = page;
 	return 0;
--
2.33.0.rc1.237.g0d66db33f3-goog